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Ising model

A fully connected Ising machine using standard technology

Nature Reviews Physics volume 6, page 533 (2024)Cite this article

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The idea behind Ising machines is elegant: take a large optimization problem that’s difficult to solve on a traditional computer, map it onto an Ising Hamiltonian, implement that Hamiltonian in a physical system, and read out the ground state, which maps back to the solution to the original problem. Ideally, this approach has benefits in terms of both speed and energy efficiency. However, reality poses complications. Practical optimization problems often map on to Hamiltonians with large numbers of spins and interactions, whereas typical Ising machines to date are small and relatively sparsely connected. There are some ways around this issue that involve decomposing the problem into smaller parts and duplicating spins (two schemes for doing so are pictured). Taking a different approach, writing in Nature Electronics, Hao Lo and colleagues report a proof-of-concept Ising solver chip that has 48 ‘spins’ with all-to-all coupling, using standard complementary metal–oxide–semiconductor (CMOS) technology.

The chip is tested on 20 randomly generated Ising models, by comparing its solutions to the best solutions found via a classical algorithm. The Ising machine performs noticeably better on problems with more densely connected spins, and somewhat better on smaller rather than larger numbers of spins. The performance doesn’t depend on temperature between –40 °C and 90 °C. The power consumption of the chip is at most 105 mW, and drops for lower connection density or number of spins. The time for the chip to reach a steady state is around 1–2 µs.

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References

Original article

  • Lo, H., Moy, W., Yu, H., Sapatnekar, S. & Kim, C. H. An Ising solver chip based on coupled ring oscillators with a 48-node all-to-all connected array architecture. Nat. Electron. 6, 771–778 (2023)

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Related article

  • Mohseni, N., McMahon, P. L. & Byrnes, T. Ising machines as hardware solvers of combinatorial optimization problems. Nat. Rev. Phys. 4, 363–379 (2022)

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  1. Nature Reviews Physics https://www.nature.com/natrevphys/

    Zoe Budrikis

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  1. Zoe Budrikis
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Correspondence to Zoe Budrikis.

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Budrikis, Z. A fully connected Ising machine using standard technology. Nat Rev Phys 6, 533 (2024). https://doi.org/10.1038/s42254-024-00757-6

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